Polyacrylate rubbers having dual cure sites, when cured, exhibit good weatherability, high temperature serviceability and resistance to oil. Such rubbers are particularly suitable for use as gaskets, seals, packings, belts and hoses, particularly under-the-hood in automobiles, and for out-of-door uses such as weather stripping.
Various curing systems for compositions containing polyacrylate rubbers having dual cure sites are taught by Morris, U.S. Pat. Nos. 3,910,866, 3,912,672 and 3,919,143. However, articles fabricated from such compositions may not be completely cured and may change their properties during normal use. It is apparent that fabricated articles, depending on their intended uses, are required to meet certain specifications, and changes in properties which take the articles out-of-specification would be unacceptable. Such changes can generally be avoided by adding a post-curing step when the articles are being fabricated. However, the post-curing step can be very time consuming.
Wolf, U.S. Pat. Nos. 5,008,345 and 5,081,194, teaches a no-post-cure method for curing compositions containing polyacrylate polymers having dual cure sites, particularly halogen and carboxyl cure sites, using a metallic acid salt and an ammonium or phosphonium quaternary salt as the curing system. The compositions are shelf stable prior to curing and give products having good compression set when cured.
Scorch is the cross-linking which occurs during processing of a curable system prior to curing and is a problem encountered with reactive curing systems. A retarder can be added to the curable system to retard scorch, and De Marco, U.S. Pat. No. 5,079,304 teaches using a substituted urea as the retarding agent with the acid salt and quaternary salt curing system of Wolf. However, those curable compositions generally have insufficient scorch safety for use in high speed injection molding.
Curable compositions exhibiting improved resistance to scorch, but where compression set of the cured compositions is not adversely affected are required for high speed injection molding. The present invention provides such curable compositions.